1. Field of the Invention
The present invention relates to a toner, a developer and an image forming apparatus.
2. Description of the Related Art
Conventional electrophotographic image forming apparatus and electrostatic recording apparatus use a toner to visualize electric or magnetic latent images. For example, in electrophotography, an electrostatic image (latent image) is formed on a photoconductor and then developed with a toner to form a toner image. The toner image is generally transferred onto a recording medium such as paper and then fixed thereon by means of, for example, heating.
Image forming apparatus that perform fixing by means of heating require a large amount of electricity in the process of heating and melting a toner to fix it on a recording medium such as paper. Thus, in terms of achievement of energy saving, low-temperature fixing property is an important property of a toner.
In order to improve a toner in low-temperature fixing property, it is necessary to control thermal properties of a binder resin occupying most of the toner. However, decreasing the softening temperature of a binder resin leads to a problem that its heat-resistant storage stability is degraded. Then, in one proposed toner that contains a binder resin containing a crystalline resin as a main ingredient, the composition and thermal properties of the crystalline resin are defined to fall within specific ranges (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2010-077419). In another proposal, a toner containing, as a binder resin, two different kinds of crystalline resins having different molecular weights (crystalline polyester resins are particularly preferred) are used under specific fixing conditions (see, for example, JP-A No. 2009-014926). In still another proposal, two different kinds of crystalline polyester resins having different storage elastic moduli at 160° C. are used as a binder resin (see, for example, JP-A No. 2010-151996).
Any of these proposed techniques can improve low-temperature fixing property in some degree while maintaining heat-resistant storage stability, but use of a crystalline resin as a binder resin causes a problem of degradation in transferability.
Therefore, at present, demand has arisen for provision of a toner excellent in transferability as well as heat-resistant storage stability and low-temperature fixing property.